Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Income Tax Contingency [Line Items]
Liability for unrecognized tax benefits	$ 414		$ 414		$ 554
Unrecognized tax benefits, accrued interest	41		41		73
Unrecognized tax benefits that would impact effective tax rate	136		136		$ 233
Provision (benefit) for income taxes	273	$ 270	898	$ 947
Excess tax benefits		$ 34		$ 219
Provision for income taxes	51		51
Interest expense related to taxing authority examination	27		27
Interest expense related to taxing authority examination, net of tax	17		17
Accounting Standards Update 2016-09 [Member]
Income Tax Contingency [Line Items]
Provision (benefit) for income taxes	$ (11)		$ (129)